The American uprising against the British in Lexington, Massachusetts, was on April 19, 1775, but Patriots Day is celebrated in Massachusetts and Maine on the third Monday in April, falling this year on April 15.

"It's a day that celebrates the free and fiercely independent spirit that this great American city of Boston has reflected from the earliest days of our nation," President Obama said Monday, a few hours after a pair of bombs rocked the finish line of the Boston Marathon, killing at least three and injuring dozens more.

For many New Englanders, it is a day of pride that comes with historical re-enactments, the Boston Marathon, baseball and a day off for schools and government employees.

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Only the Waco siege and the Oklahoma City bombing actually occurred on April 19, the anniversary of the Battles of Lexington and Concord. Still, to many following developments in Boston online, the proximity of Monday's attack to the April 19 anniversaries was enough to suggest an act of domestic terrorism.

"Obviously, nobody knows anything yet," Esquire magazine's Charles Pierce said, "but I would caution folks jumping to conclusions about foreign terrorism to remember that this is the official Patriots Day holiday in Massachusetts ... and that the actual date (April 19) was of some significance to, among other people, Tim McVeigh, because he fancied himself a waterer of the tree of liberty and the like."

McVeigh and Oklahoma City bombing co-conspirator Terry Nichols were associated with the extreme right-wing and militant Patriot Movement, which rejects the legitimacy of the federal government and law enforcement. Adherents sometimes form armed militia groups and claim the right to armed self-defense against what they believe to be an oppressive government.

McVeigh said he targeted the Federal Building in Oklahoma City to avenge the raid on Waco. Despite commonly held beliefs, it's unclear whether the Columbine shooters timed that attack to mark either Adolf Hitler's birthday or the Waco incident.

Time Washington correspondent Alex Altman also noted Patriots Day's "significance" to the "militia movement" in a tweet that was shared 507 times. He also mentioned the Oklahoma City bombing anniversary. In a subsequent tweet, he clarified that "OKC was on Apr. 19, anniversary of the Battles of Lexington & Concord, which are celebrated in Mass as Patriots Day."

But is there really something about this time of the year that makes domestic terrorism more prevalent?

"I have seen nothing to suggest that anything about April itself makes people violent," Robert Blaskiewicz, who runs the blog Skeptical Humanities, said in a 2011 interview with CNN about the 20-year anniversary of the siege of the Waco compound.

"That said, the reason why we see certain types of political violence in mid- to late April is because of a few unhappy coincidences: that Waco happened to fall on the anniversary of the Battles of Lexington and Concord, the first battles in a war against a tyrannical oppressor.

"For many people who labor under the idea that the federal government is a tyrannical foreign oppressor like the British monarchy, Waco symbolizes a war of a government against its people."

In the mythology that has grown up around Waco and Oklahoma City among self-identified patriots, he said "the 19th has become a sort of high holiday for those who think that they live under the thumb of a tyranny."

But, as the injury count continues to rise in Boston, the prevailing sentiment is sorrow and solidarity.

"Don't know what to say. Everyone who grew up in and around Boston has been at the finish line on Patriots Day. Could have been any of us," tweeted Frank Dale, digital editor for ESPN's "Mike And Mike in the Morning" show.

President Obama offered a nod to the city's strength.

"Boston is a tough and resilient town, so are its people," he said. "I'm supremely confident that Bostonians will pull together, take care of each other, and move forward as one proud city.

"And, as they do, the American people will be with them every single step of the way."